Pattern formation method

ABSTRACT

A resist film is formed from a chemically amplified resist material including a phenol polymer, an acrylic polymer and an onium salt serving as an acid generator. The resist film is selectively irradiated for pattern exposure with extreme UV of a wavelength of a 1 nm through 30 nm band or an electron beam, and is developed after the pattern exposure, so as to form a resist pattern.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a pattern formation method forforming a resist pattern by selectively irradiating a resist film madefrom a chemically amplified resist material with extreme UV or anelectron beam.

[0002] In processes for semiconductor integrated circuit devices,lithography technique is desired to be further developed in accordancewith increase of the degree of integration and downsizing ofsemiconductor integrated circuits.

[0003] As exposing light employed in the lithography technique, amercury lamp, KrF excimer laser (of a wavelength of a 248 nm band), ArFexcimer laser (of a wavelength of a 193 nm band) or the like iscurrently used. For the generation of 0.1 μm or less, and particularlyof 0.05 μm or less, whole exposure to extreme UV of a wavelength (of a 1nm through 30 nm band) shorter than that of the ArF excimer laser or anelectron beam (EB) is now being examined to be employed.

[0004] In the lithography technique using extreme UV or an electron beamas the exposing light, a chemically amplified resist material with highresolution and high sensitivity is preferably used.

[0005] Therefore, in the lithography technique using extreme UV or anelectron beam, a chemically amplified resist material suitable for theArF excimer laser lasing at a wavelength close to that of extreme UV isnow being examined for use.

[0006] Now, a first conventional pattern formation method will bedescribed with reference to FIGS. 3A through 3D.

[0007] First, a chemically amplified resist material having thefollowing composition is prepared: Base polymer:poly((t-butyloxystyrene) − (hydroxystyrene)) 1.8 g (whereint-butyloxystyrene:hydroxystyrene = 40 mol %:60 mol %) Acid generator:triphenylsulfonium triflate 0.4 g Solvent: propylene glycol monomethylether acetate 20 g

[0008] Next, as shown in FIG. 3A, the chemically amplified resistmaterial having the aforementioned composition is applied on asemiconductor substrate 1 so as to form a resist film 2 with a thicknessof 0.2 μm.

[0009] Then, as shown in FIG. 3B, the resist film 2 is selectivelyirradiated for pattern exposure with extreme UV 3 (of a wavelength of a13.5 nm band) with exposure energy of 30 MJ/cm² through a reflectionmask (not shown) having a desired mask pattern. After the patternexposure, as shown in FIG. 3C, the resist film 2 is subjected topost-exposure bake (PEB) with a hot plate at a temperature of 100° C.for 60 seconds.

[0010] In this manner, an exposed portion 2 a of the resist film 2becomes soluble in an alkaline developer owing to a function of an acidgenerated from the acid generator while an unexposed portion 2 b of theresist film 2 remains insoluble in an alkaline developer because no acidis generated from the acid generator therein.

[0011] Next, the resist film 2 is developed with an alkaline developer,such as a 2.38 wt % tetramethylammonium hydroxide developer, so as toform a resist pattern 4 with a line width of 0.07 μm from the unexposedportion 2 b of the resist film 2 as shown in FIG. 3D.

[0012] Next, a second conventional pattern formation method will bedescribed with reference to FIGS. 4A through 4D.

[0013] First, a chemically amplified resist material having thefollowing composition is prepared: Base polymer:poly((t-butyloxycarbonyloxystyrene) − (hydroxy- 1.8 g styrene)) (whereint-butyloxycarbonyloxystyrene:hydroxystyrene = 35 mol %:65 mol %) Acidgenerator: triphenylsulfonium triflate 0.8 g Solvent: propylene glycolmonomethyl ether acetate 20 g

[0014] Next, as shown in FIG. 4A, the chemically amplified resistmaterial having the aforementioned composition is applied on asemiconductor substrate 1 so as to form a resist film 2 with a thicknessof 0.2 μm.

[0015] Then, as shown in FIG. 4B, the resist film 2 is selectivelyirradiated for pattern exposure with an electron beam (of 100 kV) withexposure energy of 25 μC/cm² through a mask 6 having a desired maskpattern. After the pattern exposure, as shown in FIG. 4C, the resistfilm 2 is subjected to post-exposure bake (PEB) with a hot plate at atemperature of 110° C. for 60 seconds.

[0016] In this manner, an exposed portion 2 a of the resist film 2becomes soluble in an alkaline developer owing to a function of an acidgenerated from the acid generator while an unexposed portion 2 b of theresist film 2 remains insoruble in an alkaline developer because no acidis generated from the acid generator therein.

[0017] Next, the resist film 2 is developed with an alkaline developer,such as a 2.38 wt % tetramethylammonium hydroxide developer, so as toform a resist pattern 4 with a line width of 0.06 μm from the unexposedportion 2 b of the resist film 2 as shown in FIG. 4D.

[0018] The exposure energy of the extreme UV is 30 mJ/cm² in the firstconventional method and the exposure energy of the electron beam is 25μC/cm² in the second conventional method. Thus, large exposure energy isrequired in any of the conventional methods. This is because aconventional chemically amplified resist material is not sufficientlysensitive to extreme UV or an electron beam.

[0019] Since large exposure energy is thus necessary in the conventionalpattern formation method using extreme UV or an electron beam as theexposing light, the throughput in the lithography in the semiconductorfabrication process is disadvantageously poor.

[0020] Although the exposure energy of extreme UV or an electron beamcan be lowered by increasing the amount of the acid generator includedin the chemically amplified resist material, when the amount of acidgenerator is increased, particles are unavoidably produced in thechemically amplified resist material. Therefore, the amount increase ofthe acid generator is not preferred.

SUMMARY OF THE INVENTION

[0021] In consideration of the above-described conventional problem, anobject of the invention is lowering exposure energy of extreme UV or anelectron beam used for irradiating a resist film made from a chemicallyamplified resist material.

[0022] In order to achieve the object, the first pattern formationmethod of this invention includes the steps of forming a resist filmfrom a chemically amplified resist material including a phenol polymer,an acrylic polymer and an onium salt serving as an acid generator;selectively irradiating the resist film for pattern exposure withextreme UV of a wavelength of a 1 nm through 30 nm band or an electronbeam; and forming a resist pattern by developing the resist film afterthe pattern exposure.

[0023] In the first pattern formation method, when the phenol polymer isirradiated with extreme UV or an electron beam, phenol radicals aregenerated from the phenol polymer. Since the generated phenol radicalsexcite the onium salt, an acid is generated from the onium salt.According to an experiment made by the present inventors, it has beenfound that when an acrylic polymer is included in a chemically amplifiedresist material including a phenol polymer, the amount of phenolradicals generated from the phenol polymer is increased.

[0024] Accordingly, the large amount of phenol radicals excite the oniumsalt, and hence, the amount of acid generated from the onium salt isalso increased, so as to improve the sensitivity of the resist film. Asa result, exposure energy of the extreme UV or the electron beam usedfor irradiating the resist film made from the chemically amplifiedresist material can be lowered.

[0025] In the first pattern formation method, the acrylic polymer ispreferably poly(acrylic acid) or poly(methyl acrylate).

[0026] Thus, the amount of phenol radicals generated from the phenolpolymer can be definitely increased.

[0027] The second pattern formation method of this invention includesthe steps of forming a resist film from a chemically amplified resistmaterial including a phenol polymer, an acrylic compound and an oniumsalt serving as an acid generator; selectively irradiating the resistfilm for pattern exposure with extreme UV of a wavelength of a 1 nmthrough 30 nm band or an electron beam; and forming a resist pattern bydeveloping the resist film after the pattern exposure.

[0028] In the second pattern formation method, in the same manner as inthe first pattern formation method, when the phenol polymer isirradiated with extreme UV or an electron beam, phenol radicals aregenerated from the phenol polymer, so that the generated phenol radicalscan excite the onium salt. According to an experiment made by thepresent inventors, it has been found that when an acrylic compound isincluded in a chemically amplified resist material including a phenolpolymer, the amount of phenol radicals generated from the phenol polymeris increased.

[0029] Accordingly, the large amount of phenol radicals excite the oniumsalt, and hence, the amount of acid generated from the onium salt isalso increased, so as to improve the sensitivity of the resist film. Asa result, the exposure energy of the extreme UV or the electron beamused for irradiating the resist film made from the chemically amplifiedresist material can be lowered.

[0030] In the second pattern formation method, the acrylic compound ispreferably acrylic acid or methyl acrylate.

[0031] Thus, the amount of phenol radicals generated from the phenolpolymer can be definitely increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIGS. 1A, 1B, 1C and 1D are cross-sectional views for showingprocedures in a pattern formation method according to Embodiment 1 ofthe invention;

[0033]FIGS. 2A, 2B, 2C and 2D are cross-sectional views for showingprocedures in a pattern formation method according to Embodiment 2 ofthe invention;

[0034]FIGS. 3A, 3B, 3C and 3D are cross-sectional views for showingprocedures in a first conventional pattern formation method; and

[0035]FIGS. 4A, 4B, 4C and 4D are cross-sectional views for showingprocedures in a second conventional pattern formation method.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Embodiment 1

[0037] A pattern formation method according to Embodiment 1 of theinvention will now be described with reference to FIGS. 1A through 1D.

[0038] First, a chemically amplified resist material having thefollowing composition is prepared: Phenol polymer:poly((t-butyloxystyrene) − (hydroxystyrene)) 1.8 g (whereint-butyloxystyrene:hydroxystyrene = 40 mol %:60 mol %) Acrylic polymer:poly(acrylic acid) 0.2 g Onium salt: triphenylsulfonium triflate 0.4 gSolvent: propylene glycol monomethyl ether acetate 20 g

[0039] Next, as shown in FIG. 1A, the chemically amplified resistmaterial having the aforementioned composition is applied on asemiconductor substrate 10, so as to form a resist film 11. Then, asshown in FIG. 1B, the resist film 11 is selectively irradiated forpattern exposure with extreme UV 12 (of a wavelength of a 13.5 nm band)with exposure energy of 8 mJ/cm² through a reflection mask (not shown).

[0040] After the pattern exposure, the resist film 11 is subjected topost-exposure bake (PEB) by annealing the substrate 10 at a temperatureof 100° C. for 60 seconds with a hot plate (not shown) as shown in FIG.1C. In this manner, an exposed portion 11 a of the resist film 11becomes soluble in an alkaline developer owing to a function of an acidgenerated from the onium salt (i.e., an acid generator) while anunexposed portion 11 b of the resist film 11 remains insoluble in analkaline developer because no acid is generated from the onium salttherein.

[0041] Next, the resist film 11 is developed with a 2.38 wt %tetramethylammonium hydroxide developer (i.e., an alkaline developer),so as to form a resist pattern 13 with a line width of 0.07 μm from theunexposed portion 11 b of the resist film 11 as shown in FIG. 1D.

[0042] Since the chemically amplified resist material including thephenol polymer also includes the acrylic polymer in Embodiment 1, theamount of phenol radicals generated from the phenol polymer isincreased. In accordance with the increase of the amount of phenolradicals, the amount of acid generated from the onium salt is alsoincreased, so that the sensitivity of the resist film can be improved.As a result, the exposure energy of the extreme UV used for irradiatingthe resist film 11 can be lowered from 30 mJ/cm² to 8 mJ/cm².

[0043] Embodiment 2

[0044] A pattern formation method according to Embodiment 2 of theinvention will now be described with reference to FIGS. 2A through 2D.

[0045] First, a chemically amplified resist material having thefollowing composition is prepared: Phenol polymer:poly((t-butyloxycarbonyloxystyrene) − (hydroxy- 1.8 g styrene)) (whereint-butyloxycarbonyloxystyrene:hydroxystyrene = 35 mol %:65 mol %) Acryliccompound: acrylic acid 0.3 g Onium salt: triphenylsulfonium triflate 0.8g Solvent: propylene glycol monomethyl ether acetate 20 g

[0046] Next, as shown in FIG. 2A, the chemically amplified resistmaterial having the aforementioned composition is applied on asemiconductor substrate 20, so as to form a resist film 21. Then, theresist film 21 is selectively irradiated for pattern exposure with anelectron beam 22 with exposure energy of 5 μC/cm² through a mask 23.

[0047] After the pattern exposure, the resist film 21 is subjected topost-exposure bake (PEB) by annealing the substrate 20 with a hot plate(not shown) at a temperature of 110° C. for 60 seconds as shown in FIG.2C. In this manner, an exposed portion 21 a of the resist film 21becomes soluble in an alkaline developer owing to a function of an acidgenerated from the onium salt (i.e., an acid generator) while anunexposed portion 21 b of the resist film 21 remains insoluble in analkaline developer because no acid is generated from the onium salttherein.

[0048] Next, the resist film 21 is developed with a 2.38 wt %tetramethylammonium hydroxide developer (i.e., an alkaline developer),so as to form a resist pattern 24 with a line width of 0.06 μm from theunexposed portion 21 b of the resist film 21 as shown in FIG. 2D.

[0049] Since the chemically amplified resist material including thephenol polymer also includes the acrylic compound in Embodiment 2, theamount of phenol radicals generated from the phenol polymer isincreased. In accordance with the increase of the amount of phenolradicals, the amount of acid generated from the onium salt is alsoincreased, so that the sensitivity of the resist film can be improved.As a result, the exposure energy of the electron beam used forirradiating the resist film 21 can be lowered from 25 μC/cm² to 5μC/cm².

[0050] Although a positive chemically amplified resist material is usedin Embodiments 1 and 2, a negative chemically amplified resist materialobtained by adding a crosslinking agent to a chemically amplified resistmaterial can be used instead. Examples of the crosslinking agent are asfollows:

[0051] 2,4,6-tris(methoxymethyl)amino-1,3,5-s-triazine

[0052] 2,4,6-tris(ethoxymethyl)amino-1,3,5-s-triazine

[0053] (1) Examples of the phenol polymer used in Embodiment 1 or 2 areas follows:

[0054] poly((ethoxyethyloxystyrene)—(hydroxystyrene)) (whereinethoxyethyloxystyrene: hydroxystyrene=35 mol %:65 mol %)

[0055] poly((methoxymethyloxystyrene)-(hydroxystyrene)) (whereinmethoxymethyloxystyrene:hydroxystyrene=40 mol %:60 mol %)

[0056] poly((tetrahydropyranyloxystyrene)-(hydroxystyrene)) (whereintetrahydropyranyloxystyrene:hydroxystyrene=35 mol %:65 mol %)

[0057] poly((phenoxyethyloxystyrene)-(hydroxystyrene)) (whereinphenoxyethyloxystyrene:hydroxystyrene=32 mol %:68 mol %)

[0058] poly((t-butyloxystyrene)-(hydroxystyrene)) (whereint-butyloxystyrene hydroxystyrene=30 mol %:70 mol %)

[0059] poly((t-butyloxycarbonyloxystyrene)-(hydroxystyrene)) (whereint-butyloxycarbonyloxystyrene: hydroxystyrene=30 mol %:70 mol %)

[0060] poly((t-butyloxycarbonylmethyloxystyrene)-(hydroxystyrene))(wherein t-butyloxycarbonylmethyloxystyrene:hydroxystyrene=28 mol %:72mol %)

[0061] poly(vinyl phenol)

[0062] (2) Examples of the acrylic polymer used in Embodiment 1 are asfollows:

[0063] poly(acrylic acid)

[0064] poly(methyl acrylate)

[0065] poly(ethyl acrylate)

[0066] poly(phenyl acrylate)

[0067] poly(vinyl acrylate)

[0068] poly(2-methyl-2-adamantyl acrylate)

[0069] poly(2-ethyl-2-adamantyl acrylate)

[0070] poly(mevalonic lactone acrylate)

[0071] poly(γ-butyrolactone acrylate)

[0072] poly((2-methyl-2-adamantyl acrylate)-(mevalonic lactoneacrylate)) (wherein 2-methyl-2-adamantyl acrylate: mevalonic lactoneacrylate=50 mol %:50 mol %)

[0073] poly((2-etyhyl-2-adamantyl acrylate)-(γ-butyrolactone acrylate))(wherein 2-ethyl-2-adamantyl acrylate: γ-butyrolactone acrylate=50 mol%:50 mol %)

[0074] poly((2-methyl-2-adamantyl acrylate)-(methyl acrylate)-(acrylicacid)) (wherein 2-methyl-2-adamantyl acrylate:methyl acrylate:acrylicacid=70 mol %:20 mol %:10 mol %)

[0075] poly((2-ethyl-2-adamantyl acrylate)-(methyl acrylate)-(acrylicacid)) (wherein 2-ethyl-2-adamantyl acrylate:methyl acrylate:acrylicacid=70 mol %:20 mol %:10 mol %)

[0076] (3) Examples of the acrylic compound used in Embodiment 2 are asfollows:

[0077] acrylic acid

[0078] methyl acrylate

[0079] ethyl acrylate

[0080] phenyl acrylate

[0081] vinyl acrylate

[0082] 2-methyl-2-adamantyl acrylate

[0083] 2-ethyl-2-adamantyl acrylate

[0084] mevalonic lactone acrylate

[0085] γ-butyrolactone acrylate

[0086] (4) Examples of the onium salt used in Embodiment 1 or 2 are asfollows:

[0087] triphenylsulfonium trifluoromethanesulfonate

[0088] triphenylsulfonium nonafluorobutanesulfonate

[0089] diphenyliodonium trifluoromethanesulfonate

[0090] diphenyliodonium nonafluorobutanesulfonate

[0091] di(4-t-butylphenyl)iodonium trifluoromethanesulfonate

[0092] di(4-t-butylphenyl)iodonium nonafluorobutanesulfonate

What is claimed is:
 1. A pattern formation method comprising the stepsof: forming a resist film from a chemically amplified resist materialincluding a phenol polymer, an acrylic polymer and an onium salt servingas an acid generator; selectively irradiating said resist film forpattern exposure with extreme UV of a wavelength of a 1 m through 30 nmband or an electron beam; and forming a resist pattern by developingsaid resist film after the pattern exposure.
 2. The pattern formationmethod of claim 1, wherein said acrylic polymer is poly(acrylic acid) orpoly(methyl acrylate).
 3. A pattern formation method comprising thesteps of: forming a resist film from a chemically amplified resistmaterial including a phenol polymer, an acrylic compound and an oniumsalt serving as an acid generator; selectively irradiating said resistfilm for pattern exposure with extreme UV of a wavelength of a 1 nmthrough 30 nm band or an electron beam; and forming a resist pattern bydeveloping said resist film after the pattern exposure.
 4. The patternformation method of claim 3, wherein said acrylic compound is acrylicacid or methyl acrylate.